Location: Aurora, ORAccident Number: WPR18LA057Date & Time: 01/02/2018, 0905 PSTRegistration: N2122SAircraft: CESSNA T210LAircraft Damage: SubstantialDefining Event: Landing gear collapseInjuries: 1 NoneFlight Conducted Under: Part 91: General Aviation - PersonalAnalysis The private pilot was conducting a cross-country flight. He reported that, while on the downwind leg preparing to land, he activated the landing gear extension lever but that the green DOWN and LOCKED light did not illuminate. The pilot thought that the landing gear was down but performed a fly-by near the air traffic control tower so that the controller could verify the position of the gear. The controller told the pilot that the landing gear appeared to be down. The controller then cleared the pilot for a second downwind approach and landing. The pilot stated that, while preparing to land a second time, he attempted to raise and lower the landing gear, but the green DOWN and LOCKED light again did not illuminate. The pilot looked in the airplane's landing gear mirror and saw that the gear appeared to be in the down position. During the landing roll, the right main landing gear collapsed, which resulted in substantial damage on the right side of the airplane. The pilot indicated that he had forgotten to perform the alternate landing gear extension procedure before landing, which is used when the gear will not lock into the down position.A postaccident examination of the landing gear system, which included multiple gear retraction and extension cycles with the gear locked, revealed no anomalies that would have precluded normal operation. The right main landing gear collapsed because it did not lock into place, most likely due to the overcenter drag brace not fully attaining the overcenter position. Probable Cause and FindingsThe National Transportation Safety Board determines the probable cause(s) of this accident to be:A collapse of the right main landing gear during the landing roll because the gear would not lock into place. Contributing to the accident was the pilot's failure to perform the alternate landing gear extension procedure before landing.FindingsAircraftMain landing gear - Incorrect use/operation (Cause)Gear extension and retract sys - Not used/operated (Factor)Personnel issuesForgotten action/omission - Pilot (Factor)Use of checklist - Pilot (Factor)Factual Information On January 2, 2018, about 0920 Pacific standard time, a Cessna T210L airplane, N2122S, was substantially damaged during landing following a right main landing gear collapse at Aurora State Airport (UAO), Aurora, Oregon. The private pilot was not injured. The airplane was registered to and operated by the pilot as a Title 14 Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions prevailed at the time of the accident and no flight plan was filed. The cross-country flight originated from Paine Field (PAE), Everett, Washington, about 0758, and was destined for Aurora.In a report submitted to the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), the pilot reported that while on downwind for runway 35 at UAO, he activated the landing gear extension lever, which was followed by the orange light going out, however, the green [down and locked] light did not illuminate. The pilot further reported that the gear appeared to be down. He then requested permission to perform a control tower fly-by, so the controller could observe the position of the landing gear; the controller confirmed that the landing gear appeared to be down, followed by clearing the pilot for a left downwind approach and landing. The pilot stated that while on downwind he attempted to raise and lower the landing gear, however, while the orange light would illuminate, the green light would not. The pilot opined that the gear appeared to be down as viewed from the airplane's landing gear mirror. Shortly after touchdown the right main landing gear collapsed, which was followed by the airplane swerving right and into the runway safety area. The airplane came to rest on its left main landing gear, nose gear and right wing tip. The right horizontal stabilizer and elevator sustained substantial damage. The pilot also mentioned that he forgot to perform the alternate landing gear extension procedure prior to landing.Under the supervision of a Federal Aviation Administration aviation safety inspector, a postaccident examination of the landing gear system was performed on January 8, 2018, at the facilities of Willamette Aviation, Aurora State Airport, Aurora, Oregon. The results of the examination revealed the following:The landing gear hydraulic lines, electrical wires, actuators, locks, valves and other landing gear system components were visually inspected, with no anomalies noted.The hydraulic system fluid was visually inspected, with the level of the fluid above the ADD mark as indicated on the reservoir dip stick. There were no obvious hydraulic leaks observed from any specific hydraulic component.The landing gear switch handle was in the GEAR DOWN position, and all three landing gear were visually and physically confirmed to be in the DOWN and LOCKED positions. The landing gear down lock actuators were both extended, and the locks themselves were over the lock pins in a position appropriate to "locked" in the down position, and with visually confirmed engagement.With the airplane position on the ground and resting on its landing gear, the green GEAR DOWN indicator illuminated when the master switch was positioned to ON; the hydraulic power pack ran for about one (1) second before the light came on.The airplane was jacked using tripod jacks, wing-mounted jack adapters, and a weighted tail stand. The landing gear was retracted and extended eight (8) cycles over a period of about 40 minutes, and functioned as described in the Cessna T210L maintenance manual, with positive down lock engagement. A green GEAR DOWN light indication was followed by the hydraulic pump shutting off. Both retraction and extension cycles were completed in approximately eight (8) seconds. Each of the cycles resulted in a normal gear retraction and extension cycle completion, with only slight increases in cycle times when the landing gear was de-synchronized by application of resistance to one or the other gear legs. The landing gear warning horn system was tested for proper operation, with no anomalies noted during the functionality check. All systems operated normally. The examination revealed no evidence of what precipitated the collapse of the right main landing gear during the landing roll. (For an in-depth description of the examination and testing, refer to the Aircraft and Landing Gear System Inspection/Function Report, which is appended to the docket for this report.)